Excavating a work site with a work machine to obtain a desired configuration can often be a complex process. The desired surface configuration may include a boundary surface having, for example, symmetric or non-symmetric walls, floors, ramps, or curves. An operator may control the motion of the work machine to carve out the volume defined by the boundary surfaces. Depending on the nature of the excavation, closely following these boundary surfaces with a work implement assembly of the work machine can be difficult. Accordingly, it takes a skilled operator to be able to successfully and accurately dig out an excavation having such boundary surfaces.
Some work machines have a computer system that is capable of storing the desired boundary surfaces as a predefined digging boundary. The computer system may monitor the position of the work implement assembly and limit the movement of the work implement assembly so that it does not pass through the predefined digging boundary. In so doing, an operator may more easily follow the digging boundary with the work implement assembly, without digging through it.
One work machine capable of limiting the movement of its work implement assembly is described in U.S. Pat. No. 6,415,604 to Motomura et al. This work machine may be programmed to include a height limit position, a reach limit position, and a depth limit position. As the work implement assembly is moved to these limit positions, the valves controlling the work implement assembly are automatically closed to prevent further movement. Accordingly, the work implement assembly cannot extend beyond the established limit positions.
Although useful in ensuring that the work implement assembly does not pass beyond a pre-designated limit, prior art work machines including a control system as described in the '604 patent may reduce the efficiency of the work machine when the work tool is operating near the pre-designated limit. When the work tool approaches the predetermined limit and the valves are closed, the operator may have to generate a new input instruction to continue excavation of the work site. Accordingly, these types of control systems may interrupt the work of the operator and prevent the work tool from moving easily along the limit position or boundary.
The present invention overcomes one or more of the disadvantages of the prior art.